Current tests of renal function estimate or measure glomerular function. Unfortunately, there are no accepted tests of tubular function. Therefore a more general test that assesses both glomerular and tubular function would be helpful in the following settings: (1) to accurately determine the extent of renal damage during acute renal failure as a guide to beginning specific therapy, and (2) to determine if an agent alters the rate of recovery of renal function. The purpose of these pilot studies is to develop the test, determine its validity, reproducibility, and behavior in several models of renal injury.